Maltose is a reducing disaccharide where two glucose molecules are bound together via the α-1,4 linkage, and is called as “malt sugar”. Since maltose has a reducing end, i.e., an aldehyde group, α-anomer (α-maltose) and β-anomer (β-maltose) are present as isomers. It is known that mono-hydrous crystal (hereinafter, simply called as “hydrous crystal”) and anhydrous crystal are present as crystalline maltose. Hydrous crystalline maltose is usually obtained as β-maltose, and a powdery product comprising hydrous crystalline β-maltose is produced on an industrial scale and commercialized.
While, an anhydrous crystalline maltose can be obtained from a concentrated solution with a moisture content of less than 5% (w/w) (Ref. Japanese Patent Kokoku No. 43,360/93). Since the anhydrous crystalline maltose contains 55 to 80% (w/w) of α-anomer and 20 to 45% (w/w) of β-anomer, the entity is α/β complex crystal. However, since the anhydrous crystalline maltose has a relatively high α-anomer content, it is usually called “anhydrous crystalline α-maltose” (Ref. Japanese Patent Kokoku Nos. 43,360/93 and 10,341/95). Since the anhydrous crystalline α-maltose absorbs moisture and is converted into stable hydrous crystalline β-maltose, and the resulting hydrous crystalline β-maltose does not absorb moisture under conditions of a relative humidity of 90% or lower, the anhydrous crystalline α-maltose is applied for powderizing foods containing moisture (Ref. Japanese Patent Kokoku Nos. 59,697/93 and 10,341/95). The above anhydrous crystalline α-maltose is commercialized by Hayashibara Shoji Inc., Okayama, Japan, as “FINETOSE®”.
Japanese Patent Kokoku No. 59,697/93 and J. E. Hodge et al., “Cereal Science Today”, Vol. 17, 7, pp. 180-188 (1972) disclose an anhydrous crystalline β-maltose and a method for preparing the anhydrous crystalline β-maltose by heating hydrous crystalline β-maltose under a reduced pressure for dehydration. However, since the anhydrous crystalline β-maltose has a defect of easily absorbing moisture, it has not been produced on an industrial scale yet. In the above literature by J. E. Hodge et al., it is reported that the anhydrous crystalline β-maltose, obtained by the above method, shows a melting point of 120 to 125° C. However, an anhydrous crystalline β-maltose with a melting point higher than 125° C. has been hitherto unknown.